ui: groups listing page - fallback on the first prefix instead of 'a' by default
ui: groups listing page - fallback on the first prefix instead of 'a' by default

This improves user UI experience where the listing is not empty is no
group name start by 'a|A'.

Change-Id: Icb20d60ce880f474717c3f2b69a663fab2a2d137

morucci/repoxplorer,morucci/repoxplorer,morucci/repoxplorer,morucci/repoxplorer